too many addresses in each transaction

[10_sjdovn_10]

Hello, when exploring blockchain.com there are some transaction that have many input addresses and many output addresses!
Are they transferred total amount of bitcoins from a wallet with multiple addresses ? or it is related to Coin mixing ?
any guide about Coin mixing would be appreciated i don't know what exactly it is!

[Oshosondy]

Transactiona with many inputs can even result to reducing privacy as it can lead to many addresses linked to a single transaction, that is not mixing in any way. The only way to mix bitcoin are coinjoin and using a mixer or some people will also send bitcoin to anonymous coins like monero and send it back to bitcoin. One non recommended way are exchanges, but I do not count it as mixing because exchanges are the worst and can be tracked or frezed by the exchange.

[NeuroticFish]

Hello, when exploring blockchain.com there are some transaction that have many input addresses and many output addresses!
Are they transferred total amount of bitcoins from a wallet with multiple addresses ?

This is a standard behavior of many custodian wallets and especially centralized exchanges.

Each user has his own deposit address. The money sent there becomes the property of the exchange and all the trades are made between numbers in the exchange's database.
This means that when somebody withdraws money, the exchange will send others users' deposits. This hopefully explains why more input addresses.

Then the exchange, in order to save costs, will group multiple withdrawals into one transaction, as long as the time between those withdrawals is not too big. So the bigger the exchange, the more output addresses you may find.

[ranochigo]

You won't exactly know.

Typical CoinJoin transaction has many inputs and many outputs. The outputs usually have quite a few that are of the same amount. Chipmixer also does this, but they split it into many addresses with a common denomination. You'd want to explore Wasabi wallet, they have a convenient system for the coordinator for CoinJoin.

[Charles-Tim]

Each user has his own deposit address. The money sent there becomes the property of the exchange and all the trades are made between numbers in the exchange's database.
This means that when somebody withdraws money, the exchange will send others users' deposits. This hopefully explains why more input addresses.

You are right, most of the transactions may come from centralized wallets and exchanges in order to save transaction fee, but there are some noncustodial wallets with 1 address that can have two or more inputs, or the same wallet different addresses with two or more inputs. If transaction is sent from such wallet and the inputs are spent, all the input used in the transaction will be included also and be seen on blockchain explorer.

10_sjdovn_10 should really tell us what he wants. Maybe he want to mix a coin, exchanges will be the last to come to mind, even though working like mixers. I can never even think about exchanges for mixing coins because it is centralized and account can be freezed. There are better ways like CoinJoin and making use of mixers rather than making use of custodial exchanges.

[NotATether]

Transactiona with many inputs can even result to reducing privacy as it can lead to many addresses linked to a single transaction, that is not mixing in any way.
~snip

Correction: Transactions having many inputs which are change addresses reduce privacy. Wallets and sniffers can figure out which ones they are by seeing if it repeatedly appears as the second of two outputs along with repeatedly being an input with a bunch of other of similarly identified change addresses.

Just having multiple inputs by itself does not reduce privacy, in fact that's how CoinJoin works. Inputs especially ones for addresses which haven't been used before don't give away any information.

Paradoxically, OP might have saw transactions that are part of mixers.

[o_e_l_e_o]

Just having multiple inputs by itself does not reduce privacy

It absolutely can.

Let's say I've withdrawn some bitcoin from an exchange I have completed full KYC on to address A. Let's say I've also withdrawn some bitcoin from a casino to address B. And let's say that I've also received some coins from a mixer to address C. If I then use addresses A, B and C as multiple inputs to the same transaction, then I have massively decreased my privacy, I've linked all those coins together under presumed common ownership and to my real details held by the exchange, I've completely negated the point of mixing the coins in address C, and I've revealed to the exchange that I use bitcoin for gambling and therefore might have my account locked or frozen.

[NotATether]

Just having multiple inputs by itself does not reduce privacy

It absolutely can.

Let's say I've withdrawn some bitcoin from an exchange I have completed full KYC on to address A. Let's say I've also withdrawn some bitcoin from a casino to address B. And let's say that I've also received some coins from a mixer to address C. If I then use addresses A, B and C as multiple inputs to the same transaction, then I have massively decreased my privacy, I've linked all those coins together under presumed common ownership and to my real details held by the exchange, I've completely negated the point of mixing the coins in address C, and I've revealed to the exchange that I use bitcoin for gambling and therefore might have my account locked or frozen.

Maybe the correct wording should've been "depending on your addresses' transaction history, using them all together links all that information together" because I was specifically referring to the case where people use addresses together which previously transacted with unidentifiable addresses (hence the phrase by itself. Of course you're going to get ID'd if you send bitcoins from an exchange, KYC or not.)

[bitmover]

Correction: Transactions having many inputs which are change addresses reduce privacy. Wallets and sniffers can figure out which ones they are by seeing if it repeatedly appears as the second of two outputs along with repeatedly being an input with a bunch of other of similarly identified change addresses.

I think that most important when identifying an address as change or destination is the round/precision value.
For example, if you have 2 outputs, one is 0.01 BTC  and the other is 0.00056721, the second one is obviously a change address.

Just having multiple inputs by itself does not reduce privacy, in fact that's how CoinJoin works. Inputs especially ones for addresses which haven't been used before don't give away any information.

Paradoxically, OP might have saw transactions that are part of mixers.

I agree that the number of inputs doesn't reduce privacy by itself. I have transactions from my signature campaign address that have 6-7 inputs from the same address lol
But the best practice would be to consolidate those inputs and send them to a mixer....

I believe small value inputs are a great privacy risk.. They do not reduce privacy by themselves, but they are a risk to privacy.

Signature campaign transactions are also a little "weird". They usually have 1-4 inputs and dozens of outputs. And each of those output addresses (the participants) have also uncommon transactions from those addresses, because each addresses holds dozens of inputs.

This is when we see bitcoin being used as real currency.

[o_e_l_e_o]

because I was specifically referring to the case where people use addresses together which previously transacted with unidentifiable addresses

I'm still not sure I follow you. Using multiple inputs from different addresses will always affect your privacy to some degree. Even if I give you a brand new address to send me a payment and someone else a different brand new address to send me another payment, if I l later use those two payments together in a transaction then I have revealed to both you and the other party at least one other address which I own and one other payment I have received.

For example, if you have 2 outputs, one is 0.01 BTC  and the other is 0.00056721, the second one is obviously a change address.

Except when people like me take advantage of this assumption and deliberately craft a transaction to have a nice round amount of change and an odd amount being sent to the recipient.

There are plenty of other ways to confuse this kind of analysis as well. For example, if I'm sending coins from a legacy address to a legacy address, and I redirect my change to a segwit address, then most people will conclude the addresses are the other way around, with the assumption being that the different address type is the recipient and the same address type is the change.